1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a multi function peripheral, a sheet conveyance apparatus which conveys an image-formed sheet (recording medium), and a sheet processing apparatus which performs processing to the sheet. Particularly the invention relates to the sheet processing apparatus, in which noises and vibration are suppressed, electric power consumption is saved, and productivity is improved by variably controlling a shift moving speed in a horizontal direction according to a shift amount when the sheets are automatically sorted.
2. Description of the Related Art
The sheet processing apparatus included in an image forming apparatus main body performs various kinds of processing. For example, the sheet processing apparatus bundles the plural image-formed sheets discharged from the image forming apparatus main body in each set, and the sheet processing apparatus performs saddle stitch processing to the bundled sheets. The sheet processing apparatus includes a sheet discharge tray which is moved in the horizontal direction parallel to a short side of the sheet while a sheet position is repeatedly shifted. In the sheet discharge tray (hereinafter referred to as shift movement), and the sheets or the processed sheet bundles are automatically sorted while stacked at the positions alternately offset in the horizontal direction.
However, when the shift movement of a large member such as the sheet discharge tray is alternately performed in the horizontal direction, the sheet processing apparatus is enlarged only by placing a drive mechanism of the sheet discharge tray, and the electric power consumption is also increased.
In order to solve the above problem, for example, Japanese Patent Application Laid-Open No. S61-033459 proposes the following sheet sorting device. In the sheet sorting device proposed in Japanese Patent Application Laid-Open No. S61-033459, a sheet-discharge rotating roller is rotated and the sheet is discharged to the sheet discharge tray by rotating frictional force of the sheet-discharge rotating roller, or the sheet bundle to which the saddle stitch processing or the like is performed in the sheet processing apparatus is discharged to the sheet discharge tray. In discharging the sheet, the shift movement is alternately performed in the horizontal direction by moving the rotating roller along with a rotating shaft in the direction of a rotating axial line, i.e., in the direction orthogonal to the sheet discharge direction. Therefore, the sheets or the sheet bundles are stacked on the sheet discharge tray while alternately offset in the horizontal direction.
When the rotating rollers are moved along with the rotating shafts in the axial line direction, it is necessary that the rotating rollers differ from each other in the shift amount according to a size of the sheet. However, in the conventional sheet sorting device, the speeds of the rotating rollers for discharging the sheet are set at a constant value by averaging the speeds at which the rotating rollers are moved along with the rotating shafts to alternately perform the shift movement in the horizontal direction of the rotating axial line. Therefore, there is the following problem to be solved.
In the rotating roller in which the necessary shift movement is small, the electric power consumption cannot be expected. This is because the rotating roller is set at a speed suitable for the large shift amount, even if the operating sound or the vibration of a drive mechanism can be suppressed by reducing the shift speed.
In the rotating roller in which the necessary shift movement is large, the productivity improvement cannot be expected. This is because the rotating roller is set at a speed suitable for the small shift amount, although an operating time can be shortened by increasing shift speed as much as possible to complete the shift.